a) Field of the invention
The present invention relates to a data transfer bus in a profile and/or dimension measuring system.
b) Description of the prior art
In a profile and/or dimension measuring system, it is indispensable for a future development of the system that a Z-axis counter measuring a profile in a direction of a Z axis of an object to be measured and an angle counter directly measuring angle components of an object to be measured are incorporated therein. Since, however, the data transfer bus in the conventional profile and/or dimension measuring system is a unidirectional one-to-one bus, it is necessary to add connectors each time the system is expanded, as shown in FIG. 1. As a result, problems have been encountered that the complication of hardware and the trouble of an expansion work render the expansion of the system difficult and a incorporation of a Z-axis counter and an angle counter in the system is not facilitated.
Further, in the profile and/or dimension measuring system, it is also indispensable for the development of the system that an edge detecting device such as an edge sensor or a touch probe is incorporated therein. In such a case, when the edge detecting device detects an edge of the object to be measured, it is necessary to temporarily latch measurement contents derived from individual measuring counters and to execute processing (such as printing with a printer) in accordance with the latched measurement contents. That is, when the edge is detected, it is necessary to transmit the result of the detection to individual measuring units. In this conventional system, however, there have been difficulties that since the data transfer bus is not constructed to transmit a measurement data latch signal, complete synchronization of hardware is not carried out and resultant deviation between an actual edge detection position and a latch position causes a detection error. Specifically, when the edge sensor detects the edge, this information is converted into command to be outputted to the bus and each measuring unit inputting the command latches a counter value (i.e., measurement contents) after interpreting the command For the reason of such procedure, a time lag occurs and deviation, namely, a detection error .DELTA.x is produced between the edge detection position and the latch position as depicted in FIG. 2. When a relative velocity between the edge sensor and the object increases, the detection error is so significant that it cannot be disregarded. Thus, although it is suggested that the latch signal is transmitted through other signal line, independently of the data transfer bus, such will cause a problem that hardware such as connectors, cables, etc. is complicated.
Furthermore, in the profile measuring system, it is necessary to remote-control various operations from an external portion. However, problems have been brought about that since the conventional data transfer bus is the unidirectional one such that only the measurement data can be transferred, such operation as the clear of the counter cannot be controlled by a host CPU and the like from an external portion as shown in FIG. 3. Although it is therefore considered that an independent signal line is provided inside the bus, such develops troubles that hardware is complicated and the signal line must be increased in the expansion of the system, with the result that the hardware is further complicated. In addition, while it is also suggested that a remote key is attached to each unit, such brings about problems that operability becomes poor and hardware is complicated.
Further, there has also been other problem that because the conventional data transfer bus is the unidirectional one and can transfer only the measurement data, the transfer of the measurement data is continuously made regardless of whether or not the data are required and a measurement unit must be added to the data each time as depicted in FIG. 4, with the result that its transfer efficiency is low.